Alright, let's get started with Firebase Remote Config for feature rollouts. First things first, head over to the Firebase console. You can either create a new project or pick one you already have.

Next up, you need to register your app with Firebase. Just click on the 'Add Firebase' button in the console. For Android, you'll need your app's package name. For iOS, it's the bundle ID.

Download the google-service.json for Android or GoogleService-Info.plist for iOS and drop that file into your app.

Now, let's add the Firebase SDK to your app. This means tweaking your build scripts and making some code changes.

First, grab the singleton Remote Config object. Then, set up the default config settings you've defined. These will be used until the Remote Config object fetches new settings from Firebase servers.

For Android:

FirebaseRemoteConfig mFirebaseRemoteConfig = FirebaseRemoteConfig.getInstance();
mFirebaseRemoteConfig.setDefaultsAsync(R.xml.remote_config_defaults);

For iOS:

let remoteConfig = RemoteConfig.remoteConfig()
remoteConfig.setDefaults(fromPlist: "RemoteConfigDefaults")

Head back to the Firebase Console, select your project, and open the Remote Config feature. Define the key-value pairs you want to use in your app.

Now, let's fetch those values from the Remote Config console to your app by calling the fetch method.

For Android:

mFirebaseRemoteConfig.fetchAndActivate()

For iOS:

remoteConfig.fetchAndActivate { (status, error) in
  guard error == nil else {
    print("Uh-oh. Got an error fetching remote values \(error)")
    return
  }
  if status == .activatedFetched || status == .fetchedDefault {
    print("Got values from the server")
  }
}

Firebase's fetch method stores the fetched values in a temporary area until they're activated.

For Android:

mFirebaseRemoteConfig.activateFetched();

For iOS:

remoteConfig.activate(completion: { (changed, error) in
    if let error = error {
        print("Uh-oh. Got an error activating fetched values \(error)")
        return
    }
    if changed {
        print("Values were activated")
    }
})

Once the fetched config parameters are activated, your app can start using them.

For Android:

mFirebaseRemoteConfig.getBoolean("your_key");

For iOS:

remoteConfig.configValue(forKey: "your_key").boolValue

By following these steps, you can use Firebase Remote Config to manage feature rollouts, testing new features and updates before rolling them out to everyone.